1. Field of the Invention
This invention relates to a compact zoom lens suitable for a lens shutter camera, a video camera or the like, and particularly to a compact zoom lens having four lens units as a whole in which the back focal length is shortened and the full lens length (the distance from a first lens surface to the imaging plane) is shortened.
2. Related Background Art
Recently, in lens shutter cameras, video cameras or the like, compact zoom lenses having a short full lens length have been required with the tendency of the cameras toward compactness. Among these, a relatively compact zoom lens including the standard field angle (having a focal length of the order of 50 mm as calculated in terms of a 35 mm still camera for a field angle 2.omega.=47.degree.) has been proposed by the applicant, for example, in Japanese Laid-Open Patent Application No. 63-271214 and Japanese Laid-Open Patent Application No. 64-72114.
These publications disclose a so-called three-unit zoom lens of a magnification change ratio of the order of 2 to 3 which has, in succession from the object side, a first unit of negative refractive power, a second unit of positive refractive power and a third unit of negative refractive power and in which these three lens units are moved toward the object side under predetermined conditions, whereby a magnification change from the wide angle end to the telephoto end is effected.
Generally in a zoom lens, if the refractive power of each lens unit is strengthened, the amount of movement of each lens unit for obtaining a predetermined magnification change ratio will become smaller and it will become possible to shorten the full lens length. However, if the refractive power of each lens unit is simply strengthened, it will lead to the problem that aberration fluctuation resulting from a magnification change becomes greater and it becomes difficult to obtain a good optical performance over the whole magnification change range particularly when a high magnification change of a magnification change ratio of 3 or higher is contrived.
On the other hand, zoom lenses of wide angle which are suitable as interchangeable lenses for a single-lens reflex camera and in which a lens of negative refractive power precedes have been proposed, for example, in Japanese Patent Publication No. 49-23912, Japanese Laid-Open Patent Application No. 58-95315 and Japanese Laid-Open Patent Application No. 2-63909, but these zoom lenses have been long in back focal length and considerably long in the full optical length.